The present invention relates to an occupant protection system for protecting an occupant of a vehicle.
Vehicles such as cars are generally equipped with a seatbelt system for protecting an occupant in a car collision, etc. A seatbelt system includes a seatbelt, a spool for withdrawing or retracting the seatbelt, and a drive unit for driving the spool.
It is known in the art to provide a seatbelt system using a motor as a drive unit as disclosed in Japanese Unexamined Patent Application Publication No. 11-180200 (incorporated by reference herein).
The seatbelt system of the related art includes an electrical control unit (ECU) and a detector for sensing the condition. The control unit controls the motor in response to a detection signal outputted from the detector. For example, a buckle switch is provided to detect that a tongue has been inserted into a buckle or has been drawn out from the buckle (to determine whether the seatbelt is in use or not in use). When a detection signal indicates that the tongue has been inserted into the buckle and the buckle switch is turned on, the control unit drives the motor in the direction that retracts the seatbelt to remove the looseness of the seatbelt. When a detection signal indicates that the tongue has been drawn out from the buckle and the buckle switch is turned off, the control unit drives the motor in the direction that retracts the seatbelt to store the seatbelt.
Vehicles are often constructed such that a control unit shifts to a sleep mode even when an ignition switch is in an off position, to prevent the discharge of a battery.
When there is a need to make the control unit in a sleep mode execute a specified control operation, a wake-up signal is inputted to a wake-up-signal input terminal of the control unit. For example, in the case where the control unit of the above-described seatbelt system is in a sleep mode by turning off the ignition key, with the seatbelt under use, when the seatbelt comes into a nonuse condition, the seatbelt must be retracted by driving a motor. Accordingly, even with the control unit in a sleep mode, power is continuously supplied to the buckle switch that detects the wearing of the seatbelt to input the detection signal of the buckle switch to the wake-up-signal input terminal of the control unit.
Here, a switch (referred to as “a switch having an A-contact”) is generally used as the buckle switch, which is in the closed position when the tongue is in engagement with the buckle (the seatbelt is in use) and in the open position when the tongue is out of engagement with the buckle (the seatbelt is not in use). Alternatively, a switch (referred to as “a switch having a B-contact”) is used which is in the open position when the tongue is in engagement with the buckle (the seatbelt is in use) and in the closed position when the tongue is out of engagement with the buckle (the seatbelt is not in use).
In order to stably detect that the switch has shifted from the closed position to the open position, a current of several mA must be supplied to the switch in the closed position. In other words, when a switch having the A-contact is used as the buckle switch, a current of several mA must be supplied to the buckle switch when the seatbelt is not in use. On the other hand, when a switch having the B-contact is used as the buckle switch, a current of several mA must be supplied to the buckle switch when the seatbelt is in use.
Therefore, there is a need for a technique of reducing the current to be supplied to the detector as one of the measures to reduce the discharge current from the battery, and particularly, the discharge current when the control unit is in a sleep mode.